1. Field of the Invention
The present invention relates to a control apparatus for a parallel hybrid vehicle which uses an engine and a motor for driving the vehicle. In particular, the present invention relates to a control technique for transmitting the output of an engine to driving wheels using a CVT (Continuously Variable Transmission) in a parallel hybrid vehicle.
2. Description of the Related Art
In conventional (non-hybrid) vehicles comprising engines and continuously variable transmissions, by means of detecting the amount of depression of an accelerator pedal using a throttle opening sensor, the driving force required by the drivers of the vehicles is calculated, and based on the calculation results, the engine speed and the transmission ratio are selected to smoothly drive the vehicle.
In comparison with vehicles comprising stage transmissions, because vehicles comprising continuously variable transmissions can select the optimum transmission ratio according to the condition of the vehicle, it is possible to maintain the desirable condition in which the engine can provide a higher energy efficiency. Therefore, vehicles comprising continuously variable transmissions are expected to have better fuel consumption.
However, in vehicles comprising continuously variable transmissions, the responsiveness in changing the transmission ratio is not good, there is the problem that the acceleration response when a kick down is performed is inferior to that of vehicles comprising stage transmissions.
Furthermore, because the acceleration response is not good due to the response delay in changing the transmission ratio, there is a tendency that the driver unduly depresses the accelerator pedal during the delay in the acceleration response, and that the throttle is opened wider than the driver wishes. In such cases, there arise the problems that fuel consumption is increased, exhaust gas is increased, and noise and vibration are increased.
The above problems are common to hybrid vehicles comprising continuously variable transmissions. That is, hybrid vehicles can enter into a running mode in which the vehicle is driven by the engine, and when in such a running mode using the engine, the problems due to the inferior responsiveness in changing the transmission ratio occur, similarly to those of conventional vehicles.
Also, when the running mode of a hybrid vehicle is shifted from a running mode in which the vehicle is driven by an electric motor to a running mode in which the vehicle is driven by an engine, there is the case that the transmission ratio of the transmission connected to the engine is not set to an optimum ratio. In such a case, due to the inferior responsiveness in changing the transmission ratio, the driving force for the vehicle is temporarily and suddenly changed when the running mode is shifted.
The object of the present invention is to provide a control apparatus and method for a hybrid vehicle by which smooth acceleration of the vehicle is possible without a delay in generating the driving force when requested by the driver.
In order to achieve the above object, the control apparatus according to the present invention comprises a requested torque calculating device which calculates a torque requested for driving the hybrid vehicle; and a torque control device which controls a torque generated by an engine and a torque generated by an electric motor of the hybrid vehicle based on the requested torque calculated by the requested torque calculating device. The torque control device controls the electric motor so as to generate a torque obtained by subtracting a torque to be generated by the engine from the requested torque.
According to this control apparatus, if the responsiveness in changing the transmission ratio of the transmission is poor and the torque generated by the engine becomes lower than the requested torque, the electric motor is controlled to generate the deficient (supplementary) torque, and smooth acceleration of the vehicle can be performed.
Also, even when the running mode of the hybrid vehicle is shifted from a running mode in which the vehicle is driven by an electric motor to a running mode in which the vehicle is driven by an engine, it is possible to avoid the shock due to the torque change and to shift the running mode smoothly.
Furthermore, because the acceleration response can be improved, it is possible to prevent the problem that the driver unduly depresses the accelerator pedal during the delay in the acceleration response, and that the throttle is opened wider than the driver wishes. Therefore, the increases in fuel consumption, exhaust gas, and noise and vibration due to the above problem, can be prevented.
When the requested torque is greater than the maximum torque which the engine can generate, the torque control device may control the engine so as to generate the maximum torque and may control the electric motor so as to generate a torque obtained by subtracting the maximum torque from the requested torque.
In this case, if the responsiveness in changing the transmission ratio of the transmission is poor and the torque generated by the engine becomes lower than the requested torque, the deficient torque can be generated by the electric motor, and smooth acceleration of the vehicle can be performed.
The torque control device may comprise an engine torque restricting device which restricts the torque to be generated by the engine in accordance with a predetermined condition.
In this case, the engine torque restricting device restricts the torque to be generated by the engine in accordance with a predetermined condition, and the deficient torque is generated by the electric motor, and smooth acceleration of the vehicle can be performed.
The engine torque restricting device may restrict the torque to be generated by the engine when the temperature of the catalyst provided in the exhaust system of the engine is higher than a predetermined temperature.
In this case, when the temperature of the catalyst provided in the exhaust system of the engine is higher than the predetermined temperature, the engine torque restricting device restricts the torque to be generated by the engine, and the deficient torque is generated by the electric motor. Therefore, smooth acceleration of the vehicle can be performed.
The engine torque restricting device may restrict the torque to be generated by the engine when a remaining battery charge of a power storage unit is greater than a predetermined battery charge.
In this case, when a remaining battery charge of the power storage unit is greater than the predetermined battery charge, the engine torque restricting device restricts the torque to be generated by the engine, and the deficient torque is generated by the electric motor. Therefore, smooth acceleration of the vehicle can be performed.
The engine torque restricting device may stop restricting the torque to be generated by the engine when the requested torque is greater than a predetermined torque.
In this case, when the requested torque is greater than a predetermined torque, for example, when the accelerator pedal is fully depressed, the engine torque restricting device stops restricting the torque to be generated by the engine. Therefore, even when quick acceleration is requested, acceleration of the vehicle can be performed smoothly and quickly.
The requested torque calculating device may calculate a torque requested for driving the driving wheels of the hybrid vehicle. The torque control device may comprise a conversion device which converts an engine torque to be generated by the engine to a driving wheel torque to be applied to the driving wheels based on at least a transmission ratio in a transmission which transmits the driving force from the engine to the driving wheels. Furthermore, the torque control device may control the electric motor so as to generate a torque obtained by subtracting the driving wheel torque converted by the conversion device from the requested torque.
In this case, the requested torque calculating device calculates a torque requested for driving the driving wheels of the hybrid vehicle, and the conversion device converts an engine torque to be generated by the engine to a driving wheel torque to be applied to the driving wheels based on at least the transmission ratio. Then, the torque control device controls the electric motor so as to generate a torque obtained by subtracting the driving wheel torque converted by the conversion device from the requested torque. Therefore, if the relationship between the engine torque generated by the engine and the driving wheel torque is modified due to the change of the transmission ratio, it is possible for the motor to generate a suitable torque in consideration of the modification of the above relationship. That is, the precision in controlling the motor can be improved.
Another aspect of the present invention is a hybrid vehicle comprising an engine which generates a torque for driving the hybrid vehicle; a transmission which is connected to an output shaft of the engine; driving wheels which are connected to an output shaft of the transmission; an electric motor which is connected to the driving wheels and assists the torque generated by the engine; a requested torque calculating device which calculates a torque requested for driving the hybrid vehicle; and a torque control device which controls a torque generated by an engine and a torque generated by an electric motor of the hybrid vehicle based on the requested torque calculated by the requested torque calculating device. The torque control device controls the electric motor so as to generate a torque obtained by subtracting a torque to be generated by the engine from the requested torque.
According to this hybrid vehicle, if the responsiveness in changing the transmission ratio of the transmission is poor and the torque generated by the engine becomes lower than the requested torque, the electric motor is controlled to generate the deficient torque.
Furthermore, another aspect of the present invention is a control method for a hybrid vehicle, comprising calculating a torque requested for driving the hybrid vehicle; controlling a torque generated by an engine and a torque generated by an electric motor of the hybrid vehicle based on the requested torque calculated by the requested torque calculating device; and controlling the electric motor so as to generate a torque obtained by subtracting a torque to be generated by the engine from the requested torque.
According to this control method, if the responsiveness in changing the transmission ratio of the transmission is poor and the torque generated by the engine becomes lower than the requested torque, the electric motor is controlled to generate the deficient torque, and the vehicle can be driven smoothly.